1. Field of the Invention
The invention relates generally to complex digital logic circuits and more particularly to a carry lookahead logical mechanism using affirmatively referenced pairs of similar field effect transistor transfer gates to provide carry outputs logically related to complex data inputs.
2. Description of the Prior Art
Complex logic circuits including carry-look-ahead logic circuits are well-known in the prior art, implemented in a variety of technologies. Straight-forward techniques of implementing complex logic circuits based upon Boolean algebraic statements have been described in detail. Straightforward application of these rules to implement a complex logic circuit may require great numbers of logical elements which, in turn, take up space in the circuit package and use power, often to such a degree that additional circuits are required simply to provide repowering and diagnostic capability. Special provisions are sometimes required to prevent back circuits.
Transfer gates are also known. These gates have the characteristic of switching on or off as the result of a gating pulse, and holding this condition for a period of time significant with respect to cycle time. While simple and easy to use in implementing logic, transfer gates are quite bidirectional and subject to back-circuit problems in complex circuits.